I keep fewer secrets than I used to. I have less shame. When I was young I had a lot of it, so everything seemed like something to hide. 

As for other people's secrets, they are safe with me. I despise a frivolous gossip. 

I don't really feel I keep secrets. I just live.

Some things aren't anyone's business. But also, if you are a person who punishes people for things like having the wrong thought or feeling, then you can't expect people to be open with you.

I keep secrets. Lots of it. Mostly my feelings, I'm not what others think I am, I'm what I want them to think about me. But I do it only to people who don't respect me. I guess it's a kind of gaslighting. But I keep some serious secrets about myself like @elsa said: some things aren't anyone's business, only because they would see it as some juicy gossip, something to spread around and enjoy in it and they would absolutely think what I feel or do or did was wrong. I keep secrets because that is my way of protecting myself. Other people's secrets are more than safe with me.

I keep secrets because I don't want judgment. Pretty much like you said, if I am going to be criticized for thinking or feeling something, I just won't reveal it. Same for having done something, or planning to do something, unless it's important to share regardless of the backlash. Venus Neptune, Pisces Moon - I'm sensitive. I can't just stop being hurt by other's judgments, and I also can't just live my life the way other people see fit, because then I wouldn't be true to myself, so I'm selective in what I share and it depends on with whom I'm sharing.

It depends on the subject, though. Some things are important enough to say that I am willing to lose people over it. And I have done that and lost friendships over it. Family, too. It's unfortunate, but if I feel strongly about something being wrong, I will say so, even if the subject is taboo, because sometimes people just haven't considered the alternative of what they are doing, and have been culturally brainwashed into doing something that they shouldn't. And here I am talking in circles all around it, hahaha, because this isn't my audience, so paragraph 1 applies here. 

I keep a lot of secrets, mine, and others too. Secrets people share with me are safe with me. I don't share my secrets because I'm not feeling the need to share much about myself. I have a 12 house sun, so exposing my personality or secrets does not come naturally to me outside my circle.